Carbon-13 NMR

In this post we will discuss about ¹³C NMR. This topic is well covered under Spectroscopy. It is one of the most important topic as per CSIR syllabus. Under this post we will discuss some basics of ¹³C NMR and at the end of the post there are some Problems related to the topic asked previously in CSIR Examinations.

What is ¹³C NMR?

Nuclear Magnetic Resonance (NMR) spectroscopy has become the dominant method of analysis for organic compounds, because in many cases it provides a way to determine an entire structure using one set of analytical tests. It is also increasingly used in inorganic chemistry and biochemistry, where it also provides a lot of valuable structural information.

Nuclear Magnetic Resonance (NMR) Spectroscopy is not limited to the study of protons. Any element with a nuclear spin (¹³C, ¹⁷O, ¹⁹F, ³¹P and many others) will give rise to an NMR signal.Carbon-13 NMR (¹³C NMR or referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy applicable to carbon. It is similar to proton NMR (1 H NMR) and allows the identification of carbon atoms whereas in other identification of H. As such ¹³C NMR is an important tool in chemical structure elucidation in organic chemistry. ¹³C NMR detects only the 13C isotope of carbon, whose natural abundance is only 1.1%, because  the main carbon isotope, 12 C, is not detectable by NMR since it has zero net spin.



Some of the properties of ¹³C NMR:

• ¹³C has only about 1.1% natural abundance (of carbon atoms)
• ¹²C does not exhibit NMR behaviour (I=0)
•  ¹³C nucleus is also a spin 1/2 nucleus
• ¹³C nucleus is about 400 times less sensitive than H nucleus to the NMR phenomena
• Due to the low abundance, we do not usually see ¹³C-¹³C coupling
• Chemical shift range is normally 0 to 220 ppm
• Chemical shifts are also measured with respect to tetramethylsilane, (CH₃)₄Si (i.e. TMS)
• Similar factors affect the chemical shifts in ¹³C as seen for H-NMR
• Long relaxation times (excited state to ground state) mean no integrations
• "Normal" ¹³C spectra are "broadband, proton decoupled" so the peaks show as single lines
• Number of peaks indicates the number of types of C

Additional Detailed Notes on this topic is provided below:

Note: these notes belong to MIT University and These are posted here just for a detailed overview of the topic.


MUST VIEW:
Practice Problems on Spectroscopy
Isolobal Analogy
18 el

This is sample image of Notes, Full notes can be downloaded from below link

Download Notes on ¹³C NMR Spectrascopy  Click Here

Practice Problems on ¹³C NMR Spectroscopy

 Ques.1: Predict the number of ¹³C NMR signals in the following compounds:

1. Benzene
2. naphthalene
3. Anthracene
4. pentacene
5. cyclohexane
6. salicylic acid
7. beta napthol
8. camphor
9. alpha napthol
10. di benza anthracene
11. 7-norborane
12. resorcinol
13. 2-pentanone
14. pinene
15. menthol
16. aspirin
17. alpha-terpenol
18. citral
19. vanilin
20. toulene
21. 4-chloro benzonitrile

 Questions Asked In CSIR NET JRF, GATE and other Examinations:

[CSIR JUNE 2012]
The number of signals that appear in broad band decoupled ¹³C NMR spectrum of  phenanthracene and anthracene is:  

 

[CSIR JUNE 2012]

 [CSIR DEC 2014]

  [CSIR JUNE 2014]

 [CSIR JUNE 2013]

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